Engraving system for producing a screened rotary printing matrix with a variable diameter

ABSTRACT

An engraving apparatus for producing a printing cylinder with an electron beam, a device for producing the beam and having a vacuum chamber housing, the vacuum chamber housing forming a gap with the cylinder during engraving, the lower part of the housing being removable and has a curvature to fit a predetermined cylinder size to form a gap therewith.

5 J a19-121 en g3,- 1 g M11204 DR- 3-18161699' 1 Unlted States Patent 1191 1111 3,816,699 Wellendorf et al. [4 June 11, 1974 ENGRAVING SYSTEM FOR PRODUCING A SCREENED ROTARY PRINTING MATRIX [56] References Cited WITH A VARIABLE DIAMETER v UNlTED STATES TE [75] Inventors: Klaus Wellendorf, Kitzeberg bei 3,136,883 6/l964 Radtke 219/121 EB Kiel; Peter Padberg, Preetz; Bernd 3,678,241 7/1972 Erlandson 219/72 Struck, Kiel, all of Germany Primary Examiner.l. V. Truhe [73] Asslgnee' gg' f GmbH Kiel Assistant Examiner-G. R. Peterson Attorney, Agent, or FirmErnest F. Marmorek [22] Filed: Feb. 13, 1973 211 Appl. No.1 332,128 1 ABSTRACT An engraving apparatus for producing a printing cylinder with an electron beam, a device for producing the [30] Foreign Application pnomy Data beam and having a vacuum chamber housing, the vac- Feb. I5, 1972 Germany 2207090 uum chamber housing forming a g p with the cylinder during engraving, the lower part of the housing being removable and has a curvature to fit a predetermined 11 1581 Field of Search 219/121 EB, 121 EM, 136, Cylmde form a erewth 219/72, 74; 250/491, 492, 427; 90/13 R 5 Claims, 2 Drawing Figures ENGRAVING SYSTEM FOR PRODUCING A SCREENED ROTARY PRINTING MATRIX WITH A VARIABLE DIAMETER CROSS-REFERENCE RELATED APPLICATIONS Reference is had to my co-pending US. Pat. application Ser. No. 332,129 filed Feb. 13, 1973.

FIELD OF THE INVENTION BACKGROUND OF THE INVENTION In the printing industry it has already been known in producing screened printing matrices from the upper surface of a printing form which originally was unprocessed by using a raster so that cup-shaped recesses are engraved into the upper surface of the printing cylinder following the printing raster and, in which the depth or the volume of the cup-shaped engravings in the upper surface of the printing cylinder were given dimensions which represent the tone value which is to printed thereby. During the engravings the depth, that is, the volume of the cup-shaped engravings is controlled by the density values obtained through the electronoptical scanning of an original picture set or form which is to be reproduced such as explained in the US. Pat. application of Hans Keller et al., Ser. No. 124,864, filed Mar. I6, 1971 entitled Method For Electro- Optical Reproduction of Half-Tone Pictures and assigned to the same assignee as the present application.

For the production of the cup-shaped engravings there are several methods known according to which by means of the electronic control of the engraving instrument an appropriate quantity of material is removed from the upper surface of the printing matrix or cylinder. This can be performed by means of a cutting tool, such as a diamond stylus, the depth of penetration of which into the upper surface of the printing form or cylinder is controlled. Such method operates very cleanly. It has, however, its disadvantage in that the engraving speed due to the mechanical process of the engraving cannot meet the ever increasing requirements as to speed, in the graphic art industry.-

Another method became known according to which the cup-shaped engravings are produced on the printing cylinder by means of an exactly focused and controlled laser beam. Such method is not practical with the presently available techniques and, at the same time, it produces an unsatisfactory printing quality.

According to a recent discovery, a method is used which employs an electronic beam, as the engraving means, with which one is able to produce the necessary cup-shaped engravings reliably and, with a desired speed. This method and the associated apparatus for practicing the method generally resides in that for the processing of an object according to a desired reproduction plan, by means of a charge carrying beam the picture is recorded. More particularly, the picture is recorded by means of a TV camera and during the recording the deflecting signals used for controlling the scanning beam of the TV camera tube are used simultaneously for the synchronized deflection of the charge carrying beam which is processing the object to be reproduced. At the same time the video-signals delivered from the TV camera are used to control the intensity of the charge carrying beam falling on the object under processing. With the help of such method satisfactory cup-shaped engravings can be made, however, one cannot attain a desirable engraving speed notwithstanding the fact that the fact that the electronic beam can be very quickly deflected within a vacuum chamber into which the workpiece is also placed. It has been found that only very few cup-shaped engravings can be made, since in the apparatus proposed by such method the advancing of the printing matrix or cylinder is slow. Probably a speed could be attained with such method if the vacuum chamber would be dimensioned so large that the printing matrix could be passed within the vacuum chamber with a desired speed in front of the system producing the electron beam. This would, however, require an enormous out-lay respecting the size of the vacuum chamber, since the printing cylinder has a length of several meters and also a large diameter. Also the mounting and removal of the printing cylinder into and out of the vacuum chamber would require long idle machine times, to which the time required for the evacuation of the chamber is still to be added.

Also a further engraving system has been proposed in which the electron beam producing system is placed within a bell-shaped vacuum chamber which is open in the direction facing the upper surface of the printing cylinder and, which forms a gap with the upper surface of the printing cylinder.

With such arrangement, however, it is not possible to engrave cylinders having various diameters, since if the gap between cylinder surface and the vacuum system of the beam device becomes too large, then a larger capacity vacuum system would be necessary to sustain the vacuum.

One could provide a separate engraving system for each cylinder size, this would, however, mean a complete change of the engraving system, which is time consuming and would require new adjustment in the beam system.

SUMMARY OF THEINVENTION It is, therefore, an object of the present invention to provide an improved engraving system which eliminates the above described disadvantages of the known apparatus and stystems and, which permits in a simple fashion to perform the engraving of printing cylinders having different diameters with the same beam device.

According to the present invention one or several interchangeable members are provided which define the relation between the vacuum chamber and the printing cylinder when different diameter cylinders are used and, which members are provided with conical sealing surfaces with respect to the vacuum chamber housing.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more readily apparent from the following description of a preferred embodiment thereof shown, by way of example, in the accompanying drawings, in which:

FIG. 1 is a schematic representation, in section, of the engraving system and its position with respect to a printing cylinder; and

FIG. 2 is a sectional view along the line A-B in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIG. 1 illustrating an engraving system constructed according to the present invention and to be used in a manner with a printing cylinder as described in our copending US. Pat. application Ser. No. 322,129 filed Feb. 13, 1973.

The engraving system illustrated in FIG. 1 consists of a vacuum chamber housing I having the shape of a rotational body of the cylindrical type, and which is provided with suction connections 2, 3 which lead to one or several vacuum pumps, not shown in the drawings for the sake of simplicity. The chamber 1 has a central portion 4 in which the electron beam system, hereinafter described, is placed and which produces a charge carrying electron beam 5 falling on a predetermined portion of the printing cylinder 6 under engraving and performs the engraving operation. The vacuum chamber 1 has a removable lower portion 7 which by means of a pair of annular cone-shaped surfaces 8 is in gastight connection with the upper wall portions of the chamber 1. The member 7 is dimensioned to follow the contour of the upper surface of the printing cylinder 6 and, according to the present invention, it can be exchanged for another member 7 having a curvature to follow the appropriate curvature of a new printing cylinder having a different diameter and which is to be used at that process. The dimensioning of the exchangeable member 7 is such that there is always a defined gap 9 formed between the vacuum chamber housing 1 and the printing cylinder 6 nothwithstanding the fact that the diameter of the printing cylinder has changed. Such a gap 9 is dimensioned so that a sufficient vacuum is always present within the vacuum chamber 1 and substained by the vacuum pumps at a level which assures a reliable operation of the electron beam 5.

With reference to FIG. 2 illustrating a section through the vacuum chamber 1 along the line A B in the FIG. 1, it is seen that the center portion 4 of the vacuum chamber 1 accomodates the electron beam. In order to increase the solidity of construction of the vacuum chamber 1, there are provided stiffening ribs 10 extending to the beam housing wall 4a. In order that the material which has been removed by the electron beam 5 during the engraving process would not enter the central portion 4 and 4a of the vacuum chamber 1, on the lower end of the vacuum chamber 1 there is provided an exchangeable electron-passing foil 41 covering the vacuum chamber 1. Such foil 41 can be secured in its place by means of annular clamping means 42 securing it on the central portion 4a of the vacuum chamber l.

I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

Having thus described the invention, what I claim as new and desire to be secured by Letters Patent, is as follows:

1. An engraving system for producing screened printing matrices on printing cylinders of different diameters, comprising, in combination:

a vacuum chamber housing comprising a vacuum chamber having a reduced pressure, a housing member having an opening defined therein in the part thereof in the direction of the upper surface of a printing cylinder and having at the opening a curvature conforming to said printing cylinder and coupling means for removably coupling said housing member to said vacuum chamber, electron beam means for producing an electron beam for performing the engraving operation on said printing cylinder, said electron beam means being located within said vacuum chamber housing, said electron beam being directed towards the opening of said vacuum chamber housing, and means for defining a predetermined gap between said housing member and said printing cylinder.

2. The engraving system as claimed in claim 1, wherein said coupling means is an annular cone-shaped projection formed on said housing member for forming a gas-tight coupling for said vacuum chamber.

3. The engraving system as claimed in claim 1, wherein said vacuum chamber comprises a central portion guiding the electron beam, the dimensions of said gap being such that the reduced pressure of said vacuum chamber is sustained enabling a reliable operation of said electron beam means.

4. The engraving system as claimed in claim 3, wherein said housing means comprises stiffening ribs for abutting said central portion of said vacuum chamber containing said electron beam guiding means.

5. The engraving system as claimed in claim 1, wherein means are provided for sealing said central portion of said vacuum chamber against spattering material during the engraving process.

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1. An engraving system for producing screened printing matrices on printing cylinders of different diameters, comprising, in combination: a vacuum chamber housing comprising a vacuum chamber having a reduced pressure, a housing member having an opening defined therein in the part thereof in the direction of the upper surface of a printing cylinder and having at the opening a curvature conforming to said printing cylinder and coupling means for removably coupling said housing member to said vacuum chamber, electron beam means for producing an electron beam for performing the engraving operation on said printing cylinder, said electron beam means being located within said vacuum chamber housing, said electron beam being directed towards the opening of said vacuum chamber housing, and means for defining a predetermined gap between said housing member and said printing cylinder.
 2. The engraving system as claimed in claim 1, wherein said coupling means is an annular cone-shaped projection formed on said housing member for forming a gas-tight coupling for said vacuum chamber.
 3. The engraving system as claimed in claim 1, wherein said vacuum chamber comprises a central portion guiding the electron beam, the dimensions of said gap being such that the reduced pressure of said vacuum chamber is sustained enabling a reliable operation of said electron beam means.
 4. The engraving system as claimed in claim 3, wherein said housing means comprises stiffening ribs for abutting said central portion of said vacuum chambEr containing said electron beam guiding means.
 5. The engraving system as claimed in claim 1, wherein means are provided for sealing said central portion of said vacuum chamber against spattering material during the engraving process. 